Process control systems often employ rotary valves, such as ball valves, butterfly valves, eccentric-disk valves, eccentric-plug valves, etc., to control the flow of process fluids. Rotary valves typically include a fluid control element (e.g., a disk, a ball, etc.) disposed in the fluid path and rotatably coupled to the body of the valve via a shaft. To control the flow of fluid through some rotary valves, the position of the fluid control element may be varied from a closed position at which the fluid control element is in sealing engagement with a seal that surrounds a flow aperture, thereby preventing fluid flow through the flow aperture, to a fully open or maximum flow rate position at which the fluid control element is spaced away from the seal, thereby allowing fluid flow through the flow aperture.
To enable the fluid control element to properly align with the seal, some rotary valves include one or more bearings. One known bearing is made of plastic (e.g., PEEK) and has a curved surface that is seated against a corresponding curved surface of the valve body. However, this curved surface, by having a complex geometry, complicates manufacturing, thereby increasing manufacturing cost. Moreover, in certain applications (e.g., under high pressures), such a bearing cannot tolerate or accommodate a thrust load (i.e., an axial load) while at the same time being subject to a torsional load (e.g., when the fluid control element is opening under pressure). Instead, when the curved plastic bearing is axially loaded while a torsional load is applied, the combined load causes the bearing to move in the axial direction, thereby unseating the bearing from the curved surface of the valve body and forcing the bearing into contact with other portions of the valve. Over time, the combined loading will cause the bearing to crack, leading to failure.